Generally the exhaust systems of internal combustion engines particularly of motor vehicles have hitherto comprised the exhaust manifold which collects the exhaust gases from the cylinders of the engine, a muffler forming an acoustic damping device connected to this manifold, e.g. via an exhaust pipe, and a tail pipe connected to the muffler and discharging the exhaust gases into the atmosphere.
The muffler may be provided with a tubular housing which can have inlet and outlet fittings connected respectively to a casing or chamber which can be referred to as the expansion chamber and to the tail pipe opening rearwardly of the vehicle. In such systems, therefore, two housings were provided, one for the expansion chamber and the other containing the sound damping means, the two housings being spaced apart in the direction of flow of the exhaust gas.
The expansion chamber has as its principal function, reduction in the energy of the outflowing exhaust gas. This is done by creating in the exhaust gas vortices or turbulence generally by baffling the flow back and forth. The muffler or sound-damping unit is intended to reduce the acoustic output which results upon the discharge of the engine gas to the atmosphere.
A tubular muffler may contain a filtering body which is permeable to the exhaust gas and through which the exhaust gas passes.
The filtering body may be composed of rock wool. The elements of the exhaust system are suspended, e.g. by yieldable elements, on the underside of the chassis of the vehicle. The pipes are composed of steel and the casings, which generally are cylindrical, are also composed of steel sheet assembled by soldering or welding and/or by rivets.
The vibration acting upon these elements of the exhaust system cooperates with the corrosive effect of the combustion gases and condensate therefrom to cause more or less rapid deterioration of the parts of the exhaust system so that the latter require frequent changing. This, of course, results in a considerable increase in the cost of maintaining an automatic vehicle. In addition, because these elements project from the bottom of the vehicle, they are subject to road hazards and hence mechanical damage.
In the British Pat. No. 360,540 and the German Pat. No. 1,113,119, there are described exhaust systems which are intended to eliminate these drawbacks. In these systems, the two housings are composed of a molded material resistant to corrosion by the exhaust gases, each housing being equipped with a removable cover enabling access to the interior and attached to the body of the housing by appropriate means. The "molding" was generally a "die casting".
In these systems, the two housings were far more durable than the earlier systems, could have any desired configuration and could conform to recesses or the like in the lower part of the chassis of the vehicle so that they could be located at greater distances from the ground and, in general, in positions less vulnerable to road hazards or the like. The baffles of the first or expansion chamber were generally molded in place with the remainder of the body and thus had unchangeable positions and fixed effects upon the gas.